Leakage monitoring of air conditioning systems

ABSTRACT

A device for detecting a leakage in a motor vehicle air conditioning system that utilizes carbon dioxide as the cooling material is provided. The device for detecting leakage includes: at least one sensor for rapid detection of especially high rate of increase of the carbon dioxide concentration and/or particularly high carbon dioxide concentration in the air of the passenger compartment; an evaluation device for evaluating the ascertained rate of increase and/or concentration; and at least one actuator which, in the case that the rate of increase and/or concentration exceeds a threshold value, performs a remedial action. The remedial action includes: carrying out forced ventilation measures of the passenger compartment; closing the ventilation channels that lead into the inner space of the vehicle; and/or separating off that part of the air conditioning system which is in contact with the air in the passenger compartment from the part of the air conditioning system that is not in contact with the air in the passenger compartment.

FIELD OF THE INVENTION

[0001] The present invention relates to a device for detecting a leakage in a motor vehicle air conditioning system that uses carbon dioxide as the cooling means.

BACKGROUND INFORMATION

[0002] In conventional automobile air-conditioning systems, R1341 (Frigen) is converted to 8744 (carbon dioxide=CO₂) as the cooling material. In case of leakage in the circulation system for the cooling material, a life-threatening CO₂ concentration can develop in the passenger compartment. As compared to R134a air conditioning systems, the probability of leakage is greater in the above-described automobile air-conditioning systems, since considerably higher pressures (up to approximately 130 bar) exist in the circulation system for the cooling material. Therefore, in case of leakage, high CO₂ concentrations (up to approximately 30 percent by volume) are created in a very short time in the passenger compartment.

[0003] It has been shown that, even in normal operation of an air conditioning system, high CO₂ concentrations may be created in the passenger compartment by closing the re-circulation vent when there are many passengers. Since CO₂ in higher concentrations is able to cause impairment of the driving ability of the driver, the CO₂ level in the vehicle should be monitored. This monitoring is also known as “air hygiene monitoring.” For example, German patent application DE 196 29 320 discusses air hygiene monitoring in the context of forced airing of inhabitable recreational vehicles. In the system discussed in published German patent document DE 196 29 320, at least one ventilation channel leading to the outside of the recreational vehicle is designed so that for each ventilation channel a controllable closure device is provided, which is designed as closure cap or louver, and which is able to be closed automatically in response to the movement of the recreational vehicle.

[0004] Published German patent document DE 197 45 645 discusses an air-conditioning system for a motor vehicle, which air-conditioning system switches over between an inside air circulation operation and an outside air introduction operation, based on the pollution of the outside air. In this system, the inside air circulation operation cannot be maintained for too long a time span.

SUMMARY OF THE INVENTION

[0005] The present invention provides a device for detecting a leakage in a motor vehicle air conditioning system that utilizes carbon dioxide as the cooling material. The device for detecting leakage includes: at least one sensor, which is designed for the particularly rapid detection of especially high rate of increase of the carbon dioxide concentration and/or particularly high carbon dioxide concentration of the inside air in the passenger compartment; an evaluation device for evaluating the ascertained rate of increase and/or concentration; and at least one actuator which, in the case that the rate of increase and/or concentration exceeds a threshold value, performs a remedial action. The remedial action includes: carrying out forced ventilation measures of the passenger compartment; closing the ventilation channels that lead into the inner space of the vehicle; or separating off that part of the air conditioning system which is in contact with the air in the passenger compartment from the part of the air conditioning system that is not in contact with the air in the passenger compartment. In this manner, the effect of a leakage is able to be substantially alleviated.

[0006] One embodiment of the present invention includes a photometric sensor, whereby an especially great measuring accuracy and an especially great response speed may be achieved.

[0007] In an alternative embodiment, the sensor may also be a micromechanical heat conductivity sensor. This heat conductivity sensor makes use of the simple physical fact that the heat conductivity of air is a function of the carbon dioxide proportion in the air, because the heat conductivity of carbon dioxide is lower by a factor of approximately 1.6 than the heat conductivity of air. Therefore an increased carbon dioxide concentration in the air leads to a reduced heat conductivity.

[0008] In accordance with the present invention, a micromechanical sensor provides low weight as well as small size, which are both important criteria for applications in the automotive field.

[0009] In one example embodiment of the present invention, the sensor is designed in such a way that, within 10 seconds, a carbon dioxide concentration of 0.5 volume-per cent can be detected in the air in the passenger compartment. This requirement far exceeds the sensitivity requirements of existing air hygiene sensors. Thereby, the sensor according to the present invention may easily handle typical cases of leakage.

[0010] In another embodiment of the present invention, the sensor is designed in such a way that a carbon dioxide concentration of at least up to 3 volume-per cent can be detected in the air in the passenger compartment. This requirement also far exceeds the requirements of existing air hygiene sensors.

[0011] In contrast to the ventilation measures known in the art, the forced ventilation measures according to the present invention achieves a rapid ventilation of the passenger compartment. The ventilation measures known in the related art, such as changing the air conditioning system operation to introduce outside air, do not offer any effective remedy when the air conditioning system is leaking, since it takes too long to completely ventilate the entire air in the passenger compartment. In accordance with one embodiment of the present invention, the forced ventilation measures include: opening at least one window by a window lift; opening the sliding roof of the vehicle; or opening the convertible top of the vehicle.

[0012] In accordance with an example embodiment of the present invention, the ventilation channels leading into the inner space of the vehicle are closed at such locations so that an evaporator of the air conditioning system, that is in touch with a ventilation channel, is no longer in contact with the air of the passenger compartment. It should be noted that the evaporator is usually the most probable leakage location. The separation may be made, for example, by a spring-loaded flap.

[0013] In accordance with an example embodiment of the present invention, if the part of the air conditioning system which is in contact with the air in the passenger compartment is the evaporator, then the evaporator is segmented by at least one control valve, and the evaporator is separated from the part of the air conditioning system that is not in contact with the air in the passenger compartment, by the closing of this control valve. In this manner, the quantity of carbon dioxide that is able to reach the passenger compartment is minimized.

[0014] In accordance with the present invention, in the case that the rate of increase and/or concentration of carbon dioxide exceeds a threshold value, a warning notice is additionally given to the driver, thereby enabling a rapid reaction for the driver.

[0015] The method according to the present invention for detecting leakage in a motor vehicle air conditioning system that uses carbon dioxide as the cooling medium, includes: using at least one sensor in conjunction with an associated evaluation device, which sensor is designed for an especially rapid detection of particularly high rates of increase of the carbon dioxide concentration and/or particularly high carbon dioxide concentration in the inside air in the vehicle; for the case that the rate of increase and/or the concentration of carbon dioxide exceeds a threshold value, carrying out forced ventilation measures of the passenger compartment, closing the ventilation channels that lead into the inner space of the vehicle, and/or separating that part of the air conditioning system that is not in contact with the air in the passenger compartment from the part of the air conditioning system that is in contact with the air in the passenger compartment.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 shows a block diagram of the structure of an example embodiment of the device according to the present invention.

[0017]FIG. 2 shows a flowchart of an example embodiment of the method according to the present invention.

DETAILED DESCRIPTION

[0018] In accordance with the present invention, detection of a leakage in the circulation system for the cooling medium, e.g., CO₂, of an air-conditioning system of an automobile is made possible, and an appropriate remedial action is taken for the purpose of largely removing the safety risks created by the leak. In addition, the CO₂ level in the passenger compartment during normal operation, i.e., when no leakage exists, may be monitored in accordance with the present invention.

[0019] A block diagram of an example embodiment of the system according to the present invention is shown in FIG. 1. In this context, block 100 includes one or several CO₂ sensors, which are suitable for detecting particularly high CO₂ rates of rise and CO₂ concentrations. The output signals of block 100 are passed on to block 101, which includes one or more evaluation circuits. Their output signals representing the measured CO₂ levels or CO₂ rising rates are passed on to a control unit 102. If there is a high CO₂ concentration, this triggers a forced ventilation via actuators 103 and 104. Additionally, via block 105 a warning signal or a warning notice is given out. In addition, a compartmentalization device or a shutoff device may be closed, for example, in the ventilation channel or in the evaporator, using one of the actuators.

[0020] There are various measuring systems for measuring the CO₂ level, which include, for example: photometric gas sensors, which are CO₂ wavelength-specific absorption filters having a bandpass at approximately 4.3 μm; chemical gas sensors, e.g., metal-oxide semiconductors, potentiometric sensors, and amperometric sensors; and heat conductivity sensors, which utilize change in the heat conductivity by CO₂. Because of the measuring stability, high sensitivity and selectivity, photometric gas sensors are utilized in an example embodiment of the system according to the present invention.

[0021] In accordance with the present invention, in addition to performing monitoring of cooling-agent leakage in R8744 air conditioning systems for automobiles, additional monitoring of air quality inside the vehicle may be carried out using the CO₂ sensors of the leakage monitoring system. For the air quality monitoring (or “air hygiene” monitoring), it is generally sufficient to measure CO₂ concentrations between 500 ppm and 10,000 ppm (ppm=“parts per million”; 10,000 ppm=1 volume-per cent) at a resolution between 500 ppm and 1000 ppm. According to MAK guidelines (MAK=“maximum work place concentration”), the following CO₂ concentrations are given as threshold values:

[0022] 1. 5000 ppm CO₂ (long-term MAK):this concentration is permitted over a period of 7 hours.

[0023] 2. 15,000 ppm CO₂ (short-term MAK):this concentration is permitted over a period of 30 minutes.

[0024] 3. 30,000 ppm CO₂:the highest concentration permitted, this concentration is permitted for a period up to 30 seconds.

[0025] A carbon dioxide proportion of 3% in the air corresponds to the quantity of 54 grams carbon dioxide in one cubic meter of air.

[0026] When specified threshold CO₂ concentration values are exceeded, a forced ventilation is performed via actuators 103 and 104, e.g., the re-circulation vent and the window lifts of the vehicle are triggered into operation. In parallel or alternatively to the forced-ventilation measures, compartmentalization measures may also be carried out, i.e., closing the ventilation channels that lead into the inner space of the vehicle, and/or separating that part of the air conditioning system that is not in contact with the air in the passenger compartment from the part of the air conditioning system that is in contact with the air in the passenger compartment.

[0027]FIG. 2 shows the method for detecting leakage in a motor vehicle air-conditioning system that uses carbon dioxide as the cooling medium. In this context, in block 200 the carbon dioxide concentration and/or its rate of increase in the air in the passenger compartment are ascertained. Subsequently, in block 201 a query is made as to whether the carbon dioxide concentration and/or its rate of increase exceeds a respective threshold value. If the answer is no (“n”), the system branches back to block 200. If, however, the answer is yes (“y”), forced ventilation measures in the vehicle's passenger compartment or compartmentalization measures are carried out in block 202. Alternatively, or in addition, a warning notice to the passengers may also be given out. 

What is claimed is:
 1. A device for detecting a leakage in a motor vehicle air conditioning system that utilizes carbon dioxide as the cooling medium, comprising: at least one sensor for detection of at least one of carbon dioxide concentration and a rate of increase of carbon dioxide concentration in air in a passenger compartment of the motor vehicle; an evaluation device for determining at least one of whether the carbon dioxide concentration exceeds a first threshold value and whether the rate of increase of the carbon dioxide concentration exceeds a second threshold; and at least one actuator for triggering, if at least one of the carbon dioxide concentration exceeds the first threshold value and the rate of increase of the carbon dioxide exceeds the second threshold value, at least one of: forced ventilation of the passenger compartment; closing of a ventilation channel that leads into the passenger compartment; and separating a part of the air conditioning system that is in contact with the air in the passenger compartment from a part of the air conditioning system that is not in contact with the air in the passenger compartment.
 2. The device as recited in claim 1, wherein the sensor is a photometric sensor.
 3. The device as recited in claim 1, wherein the sensor is a micromechanical sensor.
 4. The device as recited in claim 1, wherein the sensor has a detection sensitivity for detecting a carbon dioxide concentration in the air in the passenger compartment that impairs at least one of health and driving attention of a driver.
 5. The device as recited in claim 1, wherein the sensor has a sensitivity for detecting, within a period of approximately 10 seconds, a carbon dioxide concentration of approximately 0.5 volume-percent in the air in the passenger compartment.
 6. The device as recited in claim 1, wherein the sensor has a sensitivity for detecting a carbon dioxide concentration of at least up to approximately 3 volume-percent in the air in the passenger compartment.
 7. The device as recited in claim 1, wherein the forced ventilation is achieved by at least one of: opening at least one window by a window lift; opening a sliding roof of the vehicle; and opening a convertible top of the vehicle.
 8. The device as recited in claim 1, wherein the ventilation channel that leads into the passenger compartment of the vehicle is closed at a location where an evaporator of the air conditioning system is operatively coupled to the ventilation channel, whereby the evaporator is no longer in contact with the air in the passenger compartment.
 9. The device as recited in claim 1, wherein an evaporator is the part of the air conditioning system that is in contact with the air in the passenger compartment, and wherein the evaporator is segmented by at least one control valve, whereby the evaporator is separated from the part of the air conditioning system that is not in contact with the air in the passenger compartment, by the closing of the control valve.
 10. The device as recited in claim 1, further comprising a warning mechanism, wherein if at least one of the carbon dioxide concentration exceeds the first threshold value and the rate of increase of the carbon dioxide concentration exceeds the second threshold value, the warning mechanism outputs a warning notice to the driver.
 11. The device as recited in claim 1, wherein the sensor is a micromechanical heat conductivity sensor.
 12. A method for detecting a leakage in a motor-vehicle air-conditioning system that utilizes carbon dioxide as the cooling medium, comprising: detecting, using at least one sensor, at least one of carbon dioxide concentration and a rate of increase of carbon dioxide concentration inside a passenger compartment of the motor vehicle; determining, using an evaluation device, whether the at least one of carbon dioxide concentration and the rate of increase of carbon dioxide concentration inside the passenger compartment exceeds a respective threshold value; and performing at least one of a plurality of remedial measures if the at least one of carbon dioxide concentration and the rate of increase of carbon dioxide concentration inside the passenger compartment exceeds the respective threshold value, wherein the remedial measures include; performing a forced ventilation of the passenger compartment; closing a ventilation channel that leads into the passenger compartment; and separating a part of the air conditioning system that is in contact with the air in the passenger compartment from a part of the air conditioning system that is not in contact with the air in the passenger compartment.
 13. The method as recited in claim 12, wherein the forced ventilation is achieved by at least one of: opening at least one window by a window lift; opening a sliding roof of the vehicle; and opening a convertible top of the vehicle. 